ASTRONOMY. IQQ 



Wo lenrn from Nature that M. Cliailea Foil lias, after soiric years' ab- 

 sence, returned to the active management of his celebrated manufact- 

 ory of optircal glass in Paris, the new firm being "Fell pt;re et Man- 

 tois." M. Feil is grandson to M. Guinand, who, some sixty years since, 

 by a mode of working almost identical with that adopted by the cele- 

 brated potter, Palissy, overcame the serious obstacles whicli occur in 

 securing the perfect homogeneity of both crown and flint glass, and 

 whose secrets have descended to his grandson. [The Nation.) 



LasseWs 2foot reflector at Greeuicich. — The new dome for this telescope 

 was completed by Messrs. T. Cooke & Sons at the (Mid of last ]\Iarch, 

 and is in ever\' respect satisfactory. It is 30 feet in diameter, covered 

 with papier-machd, on an iron frame-work, an<l turns with great ease. 

 The shutter-o])euing extends from beyond the zenith to the horizon and 

 is closed by a single curved shutter (3 feet inches wide at the zenith 

 and 6 feet wide at the horizon), which turns about a point in the dome- 

 curb opposite to the shutter-opening, and runs on guiding-rails at the 

 horizon and near the zenith, the curved shutter being continued by an 

 open frame- work to complete the semicircle. This arrangement appears 

 to leave nothing to be desired as regards ease of manipulation. The 

 equatorial has required a number of small repairs and general clean- 

 ing, some i)arts of the mounting having been probably strained in 

 process of removal, and the bearings in particular having suffered from 

 Avear and subsequent disuse, so that it has been necessary to raise the 

 instrument and regrind these in several instances. The mirror has 

 been cleaned, and appears to be in very good condition as regards pol- 

 ish. The definition on stars seems to be very good as far as it has been 

 practicable to test it before the mounting of the telescope has been put 

 into proper order. The delay in the comi)letion of the dome has nec- 

 essarily delayed the work on the instrument, which is now raj^idly ad- 

 ancing to completion. {Nature.) 



J)r. H. G. VogeVs opinion of the objective of the great Vienna refractor. — 

 " In the spring months (1>S83), when there were several consecutive days 

 of exquisitely clear weather, I got the impression that the objective was 

 rather good, but that the images as regards sharpness were not to be 

 compared with those of middle-sized instruments, and on leaving Vienna 

 I had formed the opinion that the difficulty of producing so large ob- 

 jectives had not been quite surmounted, and that the advantage of large 

 objectives principally consisted in the amount of light through which 

 much detail would be revealed (though not with the sharpness of mid- 

 dle-sized instruments), which by a smaller amount of light would quite 

 escape the eye of the observer. 



"But by my observations in September this opinion was completely 

 upset. 1 have acknowledged that the Vienna objective as regards the 

 l)recision of the images leaves nothing to be desired, and that it was 

 only from want of taking the state of the air into account that I had 

 formed my former opinion. I have with advantage, on splendidly clear 



